In recent years, optical disc drives for compact discs (CD-ROM, CD-R, CD-RW, etc.) and digital versatile discs (DVD-ROM, DVD-RW, DVD-RAM, etc.) serving as music media and information recording media have rapidly become prevalent. As for optical pickups serving as key components of optical disc drives, there is an increasing demand for high power responding to high-speed recording, high-performance responding to specifications of CDs and DVDs, and miniaturization responding to low-profile optical disc drives. Therefore, for optical devices used for optical pickups, it is necessary to increase thermal dissipation of packages achieving high power, increase the number of pins to respond to high performance, and design low-profile package structures for miniaturization. Conventionally optical devices (e.g., a hologram unit) in which optical elements such as a light receiving element and a laser light emitting element are mounted on mounting substrates have been widely used.
FIGS. 11 and 12 illustrate a publicly known optical device 41. FIG. 11 is a plan view and FIG. 12 is a sectional view taken along line X-X′ of FIG. 11. The optical device 41 is constituted of a plurality of lead frames 42 having die pads and leads thereon, a resin package 43 formed by resin molding, a silicon substrate 44 having a 45-degree reflex mirror for reflecting laser light to the above of the package 43 and a circuit for receiving and processing light reflected from an optical disc, light receiving elements 45 integrated on the silicon substrate 44, a semiconductor laser 46 placed at the center of the package 43 via the silicon substrate 44, and a hologram element 47 on which grating patterns 47a and hologram patterns 47b are formed. Outer ends 42a of the lead frames 42 correspond to external wiring terminals used for connection with external equipment. The outer ends 42a are arranged in a width direction W of the package 43 and protrude to the outside of the package 43. When the optical device 41 is mounted in an optical pickup, the width direction W of the optical device 41 is equal to the thickness direction of an optical disc (not shown).
As shown in FIG. 12, emitted light 49 from the semiconductor laser 46 is reflected to the above of the package 43 by the reflex mirror of the silicon substrate 44, diffracted by the grating patterns 47a, and passes through the hologram element 47. Thereafter, the light passes through optical components (not shown) such as a collimate lens and an object lens and reaches the optical disc (not shown). Then, reflected light 50 from the optical disc returns through the same path, is diffracted by the hologram patterns 47b, and incident on the light receiving element 45.
However, for high power, high performance, and miniaturization of optical pickups, two objects have to be attained by the optical device. One object is to obtain higher thermal dissipation responding to high power and another object is to obtain a smaller pitch of the external wiring terminals (corresponding to the outer ends 42a of the lead frames 42 shown in FIGS. 11 and 12) in response to slimming down and high performance.
In general, an optical disc for high-speed recording requires high power of 200 mW or more as an optical output from a semiconductor laser unit. Accordingly, the driving current of a laser increases, the temperature of a laser device also increases, and thus the reliability of the laser decreases. Therefore, in order to stably drive the laser according to a change in ambient temperature, heat generated by the laser has to be dissipated efficiently. However, in the conventional optical device 41, the package 43 is made of a resin having a low thermal conductivity (0.5 W/m/deg), so that heat cannot be efficiently dissipated.
Packages with small widths are demanded for miniaturization of optical pickups. However, in the conventional optical device 41, the plurality of external wiring terminals (corresponding to the outer ends 42a of the lead frames 42) are arranged in the width direction W, and thus in order to increase the number of external wiring terminals to obtain high performance while responding to miniaturization, it is necessary to reduce a pin pitch (that is, a pitch between the external wiring terminals and the pin pitch corresponds to a pitch P between the outer ends 42a of the lead frames 42). The width W of the package 43 has to be set to, e.g., 3 mm or smaller for miniaturization; whereas at least 20 external wiring terminals are necessary for high performance. In this case, for example, when the width of the external wiring terminal (corresponding to the outer ends 42a of the lead frames 42) is set to 0.15 mm and the interval of the external wiring terminals is set to 0.15 mm, the pin pitch (corresponding to the pitch P between the outer ends 42a of the lead frames 42) has to be set to 0.3 mm, which is an extremely small value. Thus, the lead frame 42 becomes hard to work or a solder bridge is likely to be formed between the adjacent lead frames 42 upon mounting to external equipment, resulting in low workability and mountability.
Japanese Patent Laid-Open No. 2001-111159 discloses an optical device (semiconductor laser device) comprising a hologram element.
Therefore, an object of the present invention is to provide an optical device which can be readily mounted and achieves higher thermal dissipation, slimness with a smaller width, and a larger number of pins, and a method of manufacturing the same.